In a liquid chromatograph (LC) or a gas chromatograph (GC), a sample is introduced into a column, components contained in the sample are temporally separated and detected in turn, and a chromatogram is obtained in which the abscissa axis indicates retention time and the ordinate axis indicates signal intensity. Then, peaks are extracted from the chromatogram, the components are identified based on retention times corresponding to the positions of peak tops, and in addition, the quantities of the components are determined from the areas of the peaks.
In order to determine a peak area for the purpose of determining the quantity of a component as previously described, it is necessary to determine the baseline of a peak. However, as described in Patent Literature 1, when ascending temperature gas chromatography is performed with a GC or gradient analysis is performed with an LC to obtain a chromatogram, “baseline drift” often occurs, where the baseline changes with time.
In such a case, the baseline is not determined as a fixed value throughout the chromatogram, but a baseline is determined for each peak. A typical method is to detect the starting point and the ending point of a relevant peak on a chromatogram, and set the line segment connecting these points as the baseline of the peak. Then, the area of the section surrounded by the peak waveform between the starting point and the ending point, and the baseline, is calculated as a peak area.
Although in the above description, a chromatogram is taken as an example, baseline drift may occur similarly on waveforms obtained with the other measurement systems. For example, as described in Patent Literature 3, in spectrometry, baseline drift may occur in a difference spectrum which is a subtraction of reference data obtained with no sample placed from measurement data obtained with a sample placed, due to differences in the measurement environment (e.g., changes occurred in an optical system, temperature change) at the time of obtaining the reference data and at the time of obtaining the measurement data. Therefore, in the case of determining the baseline of a spectrum too, as in the case of a chromatogram, an influence of the baseline drift can be eliminated by performing the baseline determination for each peak in such a manner as previously described.